Bug Description

Stacktrace is visible for the api users in case some internal exception occurs. This should not be possible for both user-friendliness reasons and to limit potential security problems of revealing failing component.

Added the faulwrapper around EC2 api so that it captures any unseen
exceptions and return a graceful error back. Also changed the openstack
exception message. The actual exception message will be printed in the
logs and would not return back the user.
Removed openstack wsgi dependency from
EC2 fault wrapper. Added unit tests for
EC2 fault wrapper
Fixes bug 869132.